Hundreds of thousands of people are about to descend upon Brazil for the Olympic and Paralympic Games. A country that has reported tens of thousands of potential cases of Zika virus in the past 18 months and where local transmission is still very much on-going. The impact the virus can have on unborn babies has raised concerns with athletes and supporters. It has even led to calls for the Games to be postponed or held in another country. But is the basis of this concern well founded and what impact will Zika virus have on the Games?
For those working in the field of emerging virus research the last few years have been eventful and shocking with a steep learning curve. In 2012, clusters of severe respiratory illness began to surface in Saudi Arabia. These cases have since been attributed to a previously unknown virus, Middle-Eastern respiratory syndrome coronavirus, with new cases still being reported. The 2013-2016 Ebola outbreak in West Africa made international headlines as the number of infections initially spiralled out of control, exposing serious omissions in global public health preparedness. However, more recently the health and scientific headlines have been dominated by a virus we have been aware of for many decades but knew very little about. Zika virus, which surfaced in Brazil in 2015, is now responsible for a major epidemic in the Americas with the number of new cases rising dramatically.
The virus, first identified in Uganda in 1947, slowly moved across Africa and then the Pacific almost unnoticed before taking hold in Brazil. The presence of the virus was only detected because of a spike in the number of reported neurological disorders seen in new born babies, most notably microcephaly. This potential link ultimately led to the World Health Organisation declaring the outbreak a public health emergency of international concern in February 2016.
There is now robust evidence that Zika virus poses a health risk to women who are pregnant or planning to conceive. The latest studies suggest that infection with Zika virus can lead to neurological disorders in unborn babies in up to 13% of women who are infected during pregnancy. This risk is magnified further by the fact that the virus has been shown to be capable of being transmitted sexually. However, this only accounts for a handful of cases with the predominant mode of transmission being via a particular species of mosquito, Aedes aegypti, found in sub-tropical countries.
To mitigate these risks, basic strategies such as mosquito repellent and reducing mosquito populations, are currently available. While around 40 vaccines are in development, with two having just been approved for phase I clinical trials, we are still several years away from one being licenced for routine use. Add to this, a lack of effective drugs that can be used to treat infected individuals and it is understandable why some people might be worried.
However, it is worth reiterating that with the exception of pregnant women, Zika virus poses no risk to the health of the vast majority of people. A tiny proportion of those who do become infected may develop serious neurological complications such as Guillain Barré Syndrome but most will not even realise they had been infected by the virus. Further to this, the immune response stimulated against Zika virus will not only clear the virus from the individual but is highly likely to stop re-infections.
One of the major reasons cited for postponing or moving the Games is the possibility of athletes and spectators becoming infected and becoming carriers of the virus, back to their home countries. Mathematical models based on what we know about the spread of dengue virus, a closely related cousin of Zika virus that is also transmitted by the same species of mosquito, predict that even with half a million additional people visiting Brazil to attend the Games, only an additional 37 cases of Zika virus are likely to be 'exported' when these people return home. Of course, as we have seen in the last week with the 14 cases of locally transmitted Zika virus reported in Miami, where there is no existing immunity to Zika virus and the Aedes aegypti mosquito is present, there is always the risk that one case is all you need for the virus to spread locally in new locations.
It is worth noting that while not attracting the same level of media attention, other public health threats posed by contaminated water at aquatic venues and other infectious diseases, such as HIV and malaria, arguably pose a much greater health threat. However, fear of the unknown and a complex, emerging situation is driving peoples' concern regarding Zika virus.
The available evidence suggests that Zika virus poses a very real risk to specific sections of society and unborn babies. This is a risk that cannot be ignored. Advice from national and international public health bodies is that these people should consider postponing non-essential travel to areas where Zika virus is currently circulating. For the rest of the population, Zika virus should not be cause for concern but given the presence of other tropical diseases in Brazil appropriate advice should be sought before travel and risky behaviours avoided.